Comparisons of the primary structure of BALB/c and NZB mouse myeloma antibodies will allow estimates of the number of genes coding for heavy and light chain variable regions. The pattern of variability found by comparing heavy and light chains within a subgroup will lead to an understanding of the origin of antibody diversity. We will locate antibody structural genes on the mouse genome. The genetic analysis of the heavy chain locus will estimate the size of the variable region locus, the order of certain variable region genes, and the relationship of variable and constant region genes. The variable regions of myeloma antibodies with similar specificity will be sequenced to assess the effect of amino acid replacement on antibody specificity. We will induce plasmacytomas in NZB mice. The NZB myeloma antibodies will be characterized. The genetic control of certain characteristics unique to either NZB or C58 mice, such as their respective antibody structures and NZB autoimmunity, will be studied in (NZBxC58) "recombinant-inbred" strains.